Method of creating a pillared layered clay (PILC)

ABSTRACT

The method enables the creation of a pillared layered clay (a PILC) by contacting the clay with a pillaring precursor and delivering energy to the reaction mixture to intercalate the precursor into the clay. The pillaring precursor is an electrically neutral organometallic molecule with a carbon-metal bond which is susceptible to proton attack whereby protons donated from sites of Bronsted acidity in the clay cleave the carbon-metal bond to yield an organic fragment of the precursor and a metal-containing pillaring fragment. A preferred precursor is Ph 2  SnCl 2 .

BACKGROUND OF THE INVENTION

PILCs may have application in the manufacture of electrically-conductivepapers. A synthetic hectorite smectite clay (LAPONITE, from LaporteIndustries Ltd) is mildly conductive and is used commercially in themanufacture of certain papers, both to pigment the paper and give itconductivity. It is an object of the present invention to increase theelectrical conductivity of such clays as LAPONITE, while not losing anyof their other properties which give them suitability for their use inpapermaking.

In Inorg. Chim. Acta. 1987, 134, at page 99 Mandair and co-workersdescribe an attempt to increase the conductivity of LAPONITE and anatural montmorillonite by the intercalation of organic molecules.Increase of an order of magnitude in D.C. conductivity were measured.

A method of creating a PILC is disclosed in Inorg. Chem. 1989, 28,2439-2443 by Petridis, D, and his co-workers. The method involveshydrolysing dimethyltin (IV) chloride and intercalating between themolecular layers of the clay the resulting dimethyltin (IV) cation.Thereafter, tin oxide pillars in the clay are created by heating theintercalated clay with glycerol to more than 200° C.

DESCRIPTION OF THE INVENTION

It is one object of the present invention to devise a route for PILCproduction which avoids the cation exchange step or the heating steputilised in the Petridis method, so as to preserve to a greater extentthe original properties of the clay, and provide enhanced prospects forimprovement of electrical conductivity. According to the invention, thisobject is achieved by selecting as the pillaring precursor anelectrically neutral organometallic molecule with a carbon-metal bondwhich is susceptible to proton attack whereby protons donated from sitesof Bronsted acidity in the clay cleave the carbon-metal bond to yield anorganic fragment of the precursor and a metal-containing pillaringfragment.

The precursor is preferably aryl, most preferably phenyl. The metalconstituent up to now preferred is tin. Suitable molecules are:

    Ph.sub.3 SnCl, (Ph.sub.3 Sn).sub.2 O, Ph.sub.2 SnCl.sub.2

which yield SnO₂ as the pillaring molecule.

The precursor is conviently presented in a liquid alcohol carrier,conveniently ethanol. Energy to bring about the intercalation of theprecursor into the clay can be provided by mechanical shaking, but thethermal energy delivered by an ordinary domestic microwave oven hasproved extremely effective with laboratory experimental samples,yielding in 5 minutes a very substantial part of the maximumintercalation achievable with any particular sample.

As mentioned above, the clay can be a montmorillonite but is preferablya synthetic hectorite such as sodium or potassium LAPONITE.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be further described with reference to thefollowing Example and the attached accompanying drawing which showsconductivity plotted against frequency for materials 10, 11, 12 and 13.

EXAMPLE

LAPONITE clay material in its RD form, that is, free from fluoride andtetron) was obtained from Laporte Industries Ltd. Ph₃ SnCl and Ph₂ SnCl₂were obtained from Aldrich Chemical Co. Ltd. Triphenyltin oxide wasprepared by hydrolysis of Ph₃ SnCl.

To 10 cm³ of dry ethanol was added 0.3 g of the triphenyl tin oxide and1.0 g of the LAPONITE clay. In a 700 W microwave oven the mixture wassubjected to 5 one minute bursts of microwave radiation. Afterwards, 0.2g of the oxide were recovered from ethanol washings. Further experimentsusing irradiation times from 1 to 30 minutes established an optimum timeof 5 minutes.

The experiment was repeated with the other two pillaring precursors. Theresults are given in Table 1 below:

                  TABLE 1                                                         ______________________________________                                                     % Material (W/W)                                                              Intercalated                                                                    Mechanical                                                                              Microwave                                            COMPOUND       Shaking   Irradiation                                          ______________________________________                                        (Ph.sub.3 Sn).sub.2 O                                                                        10        33                                                   Ph.sub.3 SnCl  45        75                                                   Ph.sub.2 SnCl.sub.2                                                                          38        44                                                   ______________________________________                                    

To assess conductivity, pressed discs of clay (0.25 g) were used. Copperwires attached to the discs by silver-loaded epoxy resin were connectedto a digital AC impedance meter and impedance measurements taken over arange of AC frequencies from 11.7 to 100 Hz. The results are shown inthe appended drawing in the form of a graph of conductivity C against ACfrequency f in kHz. Plot 10 is of LAPONITE without intercalation. Plot11 is with intercalation by (Ph₃ Sn)₂ 0. Plot 12 is with Ph₃ SnCl andPlot 13 with Ph₂ SnCl₂.

Further analysis of the intercalated clay materials by x-ray powderdiffraction, Mossbauer spectroscopy. gas, infra-red and masnmrspectroscopy was carried out. the Mossbauer spectra suggested that allthe tin from the Ph₃ SnCl underwent conversion to SnO₂, whereas some ofthe Ph₂ SnCl₂ precursor was not converted. There wag no qualitativeanalytical evidence for liberation of sodium ions from the clay. This,together with the x-ray diffraction data on increased basal spacings inthe clay, suggested tin oxide pillar formation under ambient temperatureand pressure and without the sacrificial reaction of an exchangedcation.

A consequence of the formation of tin oxide pillars is the liberation ofbenzene, but none was found in the supernatant liquid followingintercalation, or in the clay washings. With Ph₃ SnCl, where the resultssuggested complete conversion, ⁻⁻ C masnmr data on the intercalated clayproduced a single resonance at δ=128.5 ppm (relative to Me₄ Si) whichwas attributed to benzene tenaciously held in the clay.

A possible mechanism is that of proton attack on the aryltin bond, theprotons coming from sites of Bronsted acidity within the clay.

We claim:
 1. A method of creating a pillared layered clay (PILC), saidmethod comprising the steps of:selecting as a pillaring precursor anelectrically neutral molecule containing a metal atom bonded directly toan aryl group; contacting a clay with said pillaring precursor toproduce a reaction mixture; and delivering energy to said reactionmixture to intercalate said precursor into said clay; whereby protonsdonated from sites of Bronsted acidity in said clay cleave acarbon-metal bond to yield an organic fragment of said precursor and ametal-containing pillaring fragment.
 2. A method according to claim 1,wherein said precursor is a phenyl derivative.
 3. A method according toclaim 1, wherein said precursor is a tin molecule.
 4. A method accordingto claim 2, wherein said precursor is Ph₂ SnCl₂.
 5. A method accordingto claim 3, wherein said precursor is (Ph₃ Sn)₂ O or Ph₃ SnCl.
 6. Amethod according to claim 1, wherein said precursor is presented in analcoholic liquid carrier.
 7. A method according to claim 1, wherein saidenergy is microwave energy.
 8. A method according to claim 1, whereinsaid clay is a synthetic hectorite.
 9. A method according to claim 8,wherein said clay is a sodium or potassium laponite.
 10. A methodaccording to claim 1, wherein said clay is a montmorillonite.